New particle formation (NPF) produces about 50% of the global cloud condensation nuclei in the troposphere. As such, NPF plays a crucial role in climate. Despite advancements in instrumentation capable of measuring freshly formed aerosol particles down to ~ 1 nm in diameter, the mechanisms behind NPF remain understudied due to the complex composition and chemistry of the atmosphere. Nucleation is the first step of NPF and involves gaseous precursors reacting to form stable clusters; consequently, it is essential to understand the reaction kinetics behind nucleation reactions. Controlled laboratory experiments have previously been used to examine these reactions, which can occur at extremely low reactant concentrations (i.e., parts per quadrillion level, 105 cm−3) or lower. Nucleation experiments require pristine conditions for the reactions to proceed without interference from unpredictable contaminants. Here, a low-cost flow reactor is presented that minimizes contamination and allows for nucleation kinetics to be observed. The layout and setup of an example reactor are presented with a brief discussion on how to operate the reactor to ensure cleanliness and repeatability. In addition, methods for quantifying nucleation reactants as well as analytical measurement techniques to adequately measure nucleation kinetics in this flow reactor system are described. This experimental protocol can be employed to characterize nucleation reactions that can ultimately be used to develop nucleation models important for predicting how aerosol particles influence climate.